Phosphorus ligands are ubiquitous in catalysis, finding use for a number of commercially important chemical transformations. Phosphorus ligands commonly encountered in catalysis include phosphines (A), and phosphites (B), shown below. In these representations R can be virtually any organic group. Monophosphine and monophosphite ligands are compounds which contain a single phosphorus atom which serves as a donor to a metal. Bisphosphine, bisphosphite, and bis(phosphorus) ligands in general, contain two phosphorus donor atoms and normally form cyclic chelate structures with transition metals. ##STR1##
Two industrially important catalytic reactions using phosphorus ligands of particular importance are olefin hydrocyanation and olefin hydroformylation. Phosphite ligands are particularly good ligands for both of these transformations. For example, the hydrocyanation of ethylenically unsaturated compounds using transition metal complexes with monodentate phosphite ligands is well documented in the prior art. See, for example, U.S. Pat. Nos. 3,496,215, 3,631,191, 3,655,723 and 3,766,237, and Tolman et al., Advances in Catalysis, 33, 1, 1985. Bidentate bisphosphite ligands have been shown to be useful in the hydrocyanation of monoolefinic and diolefinic compounds, as well as for the isomerization of non-conjugated 2-alkyl-3-monoalkenenitriles to 3- and/or 4-monoalkene linear nitriles. See, for example, U.S. Pat. Nos. 5,512,695, 5,512,696 and WO 9514659. Bidentate phosphite ligands have also been shown to be particularly useful ligands in the hydrocyanation of activated ethylenically unsaturated compounds. See, for example, Baker, M. J., and Pringle, P. G., J. Chem. Soc., Chem. Commun., 1292, 1991; Baker et al., J. Chem. Soc., Chem. Commun., 803, 1991; WO 93,03839. Bidentate phosphite ligands are also useful for alkene hydroformylation reactions. For example, U.S. Pat. No. 5,235,113 describes a hydroformylation process in which an organic bidentate ligand containing two phosphorus atoms linked with an organic dihydroxyl bridging group is used in a homogeneous hydroformylation catalyst system also comprising rhodium. This patent describes a process for preparing aldehydes by hydroformylation of alkenically unsaturated organic compounds, for example 1-octene or dimerized butadiene, using the above catalyst system. Also, phosphite ligands have been disclosed with rhodium in the hydroformylation of functionalized ethylenically unsaturated compounds: Cuny et al., J. Am. Chem. Soc., 1993, 115, 2066. These prior art examples demonstrate the utility of bisphosphite ligands in catalysis.
While these prior art systems represent commercially viable catalysts, they do suffer from significant drawbacks. Primarily, the catalyst, consisting of the ligand and the metal, must be separated from the reaction products. Typically this is done by removing the product and catalyst mixture from the reaction zone and performing a separation. Typical separation procedures involve extraction with an immiscible solvent, distillation, and phase separations. In all of these examples some of the catalyst, consisting of the ligand and/or the metal, is lost. For instance, distillation of a volatile product from a non-volatile catalyst results in thermal degradation of the catalyst. Similarly, extraction or phase separation results in some loss of catalyst into the product phase. These ligands and metals are often very expensive and thus it is important to keep such losses to a minimum for a commercially viable process.
One method to solve the problem of catalyst and product separation is to attach the catalyst to an insoluble support. Examples of this approach have been previously described, and general references on this subject can be found in "Supported Metal Complexes", D. Reidel Publishing, 1985, Acta Polymer. 1996, 47, 1, and Comprehensive Organometallic Chemistry, Pergamon Press, 1982, Chapter 55. Specifically, monophosphine and monophosphite ligands attached to solid supports are described in these references and also in Macromol. Symp. 1994, 80, 241. Bisphosphine ligands have also been attached to solid supports and used for catalysis, as described in for example U.S. Pat. No. 5,432,289, J. Mol. Catal. A 1996, 112, 217, and J. Chem. Soc., Chem. Commun. 1996, 653. The solid support in these prior art examples can be organic, e.g., a polymer resin, or inorganic in nature.
These prior art systems have to date suffered from several drawbacks and have not reached commercial potential. Among the drawbacks noted in the literature are metal leaching and poor reaction rates. In addition, the prior art systems are often not readily amenable to precise control of the ligand coordination properties, e.g., electronics and steric size. What is needed is a supported bis(phosphorus) ligand system which overcomes the problems and deficiencies inherent in the prior art. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description which hereinafter follows.